Calcium absorption by fruit and leaves of sweet cherry trees (Prunus avium L.) by isotope labeling

Abstract

In sweet cherry, foliar Calcium–based products are used to mitigate rain–cracking in fruit and to improve its firmness during storage. Information on foliar Calcium (Ca) absorption efficiency by fruit and leaves in the field is scarce. In part, this is due to the limitations of the traditional analytical techniques for assessing Ca levels in these organs. Here, we hypothesize that leaves and fruit differ in their abilities to uptake surface applications of Ca and, moreover, that their abilities are influenced by phenology. To test this hypothesis, foliar 44Ca (0.05% 44CaCl2) was used to enrich sweet cherry fruit and leaves of the combination ‘Lapins’/‘Colt’ during the 2019–2020 growing season in the Central Valley of Chile (34° 0’ S, 71° 41’ W). Six treatments were applied, represented by different timings (days after full bloom, DAFB) of isotopic labeling of either fruit or leaves. Labeling was applied at Stage I, SII and SIII of fruit development. Fruit or leaves were ‘painted’ with 44CaCl2 (0.05%, 97 atom%) using a brush. Each labeling date considered a different group of similar fruiting spurs on the two-year-old wood of individual vertical branches. Additional samples were collected to measure natural abundance of 44Ca. Labeled fruit were removed 48 h after aerial 44Ca enrichment and at harvest (87 DAFB).Uptake of 44Ca by fruit and leaves was observed throughout the period of fruit development. Fruiting spur leaves (FSL) and fruit absorbed 44CaCl2 and were highly enriched 48 h after labeling. The earlier the labeling date, the higher the 44Ca tracer recovery detected in both organs. However, FSL showed higher δ44Ca ‰, 44Ca concentrations and 44Ca contents than fruit during the whole period of fruit development. After 48 h, the aerial uptake at SI (expressed as δ44Ca ‰) was 3.4 times higher in immature FSL and 5.7 times higher in immature fruit than SIII of fruit development, which indicates that Ca sprays should start soon after fruit set. We conclude that in sweet cherry, foliar Ca is absorbed by fruit and spur leaves, but the absorption is more efficient in the early stages of fruit development and for young leaves.